Tear film assessment and dry eye Flashcards
What is the 2 layer model of the tear film?
Made up of a lipid layer and mucoaqueous layer (mucins, proteins and peptides within)
What is the definition of dry eye?
A multifactorial disease of the ocular surface caused by a loss of tear film homeostasis, where the tear film is unstable and hyperosmolar, the ocular surface is inflamed and damaged and ocular symptoms occur. Neurosensory abnormalities can play a role in the cause.
What are the types of dry eye?
ADDE (Aqueous deficient dry eye)
EDE (Evaporative dry eye)
What causes ADDE?
A lack of aqueous production or a low flow rate causes hyperosmolarity - this starts a pathway which causes damage and apoptosis to goblet cells and glycocalyx, causing tear film instability and further hyperosmolarity
What causes EDE?
A high evaporation rate of aqueous tears causes hyperosmolarity - this starts a pathway which causes damage and apoptosis to goblet cells and glycocalyx, causing tear film instability and further hyperosmolarity
What are the definite risk factors for dry eye?
CL wear
MGD
Age
Sex
Race
Connective tissue disease
Sjogren’s syndrome
VDU use
Androgen deficiency
HRT
Stem cell transplant
Environment
Medications (eg antihistamines, antidepressants)
What are some probable risk factors for dry eye?
Diabetes
Rosacea
Viral infection
Thyroid disease
Refractive surgery
Low fatty acid intake
What are some inconclusive risk factors for dry eye?
Menopause
Acne
Smoking
Alcohol
Pregnancy
Oral contraceptives
Demodex infestation
Sarcoidosis
What happens to the tear film after CL wear?
Lipid layer is thinner and less stable
Osmolarity is increased
Inflammatory mediators are increased (but inflammation is sub-clinical)
The composition of proteins and ions can be altered
The ocular surface temperature decreases
Why does the tear film need to be assessed?
Check tear film quantity and quality
Diagnose CLIDE/DE and manage
What makes it difficult to assess the tear film?
Thin
Transparent
Moving
Small volume
Easily disturbed - bright light causes tearing and blink pattern changes
What does the ideal test for tear film assessment look like?
Quick
Simple
Cheap
Accurate
Repeatable
Minimal invasion
Allows differential diagnosis
What categories of tear film assessment are there?
Invasive
Non-invasive
Direct
Indirect
Quality
Quantity
Name some examples of non invasive tear film assessment
Questionnaires
Tear meniscus height
Assessing quality
Observing lipid layer
NIBUT
Keratometer
What is a normal tear meniscus height?
0.2-0.3mm
What tear meniscus height is considered dry eye?
<0.18mm
What should you record when assessing tear film quality?
Debris
Make up
Mucus threads
Speed of movement
How do you measure NIBUT?
Project grid onto cornea
Measure time from blink to tear break up 3 times
Record median
What is normal for BUT?
20-40 secs
What BUT is considered dry eye?
<10 secs
What are lid-parallel conjunctival folds?
Folds in bulbar conjunctiva parallel to lid margin caused by friction
Name some examples of invasive tear film assessment
Tear osmolarity measurement
Schirmer test
Phenol red thread test
FBUT
Ocular surface staining
Lid wiper epitheliopathy
How is the Schirmer test carried out?
Schirmer strips inserted into lower fornix
Px closes eyes for 5 mins
Amount of tears measured
What is a normal result for the Schirmer test?
> 10mm
